Method and means for cooling compressor recycle gas



y 23 1967 E. A. HARPE 3,320,758

METHOD AND MEANS FOR COOLING COMPRESSOR RECYCLE GAS Filed June 21, 1965 FLUID TO BE REFRIGERATED EVAPORATOR INVENTOR E. A. HARPER A T TORNEKS' United States Patent a,3ze,75s METHOD AND MEANS FOR COOLING COWRESSOR RECYCLE GAS Ernest A. Harper, Bartlesville, Okla, assignor to Phillips Petroleum Company, a corporation of Delaware Filed June 21, 1965, Ser. No. 465,582 Claims. (Cl. 62117) This invention relates to a method and means for cooling .that portion of a compressor discharge gas that is recycled to the compressor suction to maintain a desired suction pressure. In one aspect the invention relates to a method and means for effecting direct heat exchange between the superheated compressor recycle gas of a refrigeration apparatus and the liquid refrigerant.

A refrigeration apparatus usually consists essentially of a compressor, a condenser and an evaporator. Refrigerant gas is compressed, cooled, condensed and then expanded in an evaporator Where heat is absorbed in the expansion of the liquid into gas. The cycle is continuous- ]y repeated. It is commonplace to operate a refrigeration apparatus so that the compressor operates intermittently or on demand. Such systems are usually thermostatically controlled and do not operate to a point where the vapor pressure in the evaporator is lower than that desired for compressor suction pressure. Home refrigerators and home air conditioners are examples of such systems.

There are systems wherein refrigeration apparatus is employed and wherein the compressor runs continuously. In such systems it is necessary to provide means for recycling compressor discharge gases to the compressor suction in order to maintain adequate suction pressure. One application of such refrigeration apparatus is the cooling of compressed hydrocarbon vapors removed from storage of liquefied hydrocarbon gases at atmospheric pressure for return to storage. In such systems there is necessarily means to recycle gas from the compressor discharge to the compressor suction. With the advent of refrigeration apparatus where Tefion rings are used in non-lubricated compressors it has been found that the Teflon rings are often damaged by recycling the hot gas from the compressor discharge.

I have discovered a simple and economical method and means for cooling the recycle gas passed directly from the compressor discharge to the compressed suction. I have found that the hot compressed gas can be cooled by direct contact with a small stream of liquid from the evaporator. Practice of the invention eliminates need for extra cooling water or expensive indirect heat exchange equipment because additional cooling water would be required to cool the bypass stream and a substantial amount of surface would be required for indirect heat exchange with liquid refrigerant. Any convenient type of liquid-gas contactor can be installed in the bypass conduit e.g. an aspirator, a gas scrubber or the like. An aspirator is a preferred apparatus because of small size, simplicity and positive action. The size of the aspirator is not critical so long as it is large enough .to supply enough liquid to cool the bypass steam at the maximum flow of bypass gas. Any excess of liquid will be dropped out in the evaporator.

A gas scrubber can be merely a reservoir of liquid for the gas to bubble through.

The flow of gas through the bypass conduit can be controlled by the pressure on the compressor suction along with means to pass a controlled amount of hot compressor gas to the compressor suction to avoid the possibility of the suction pressure becoming too low.

It is an object of the invention to provide a method and means for cooling compressor recycle gas in a refrigeration system. It is also an object of the invention to provide a method and means for contacting the com- 3,320,758 Patented May 23, 1957 pressor recycle gas in a refrigeration system with liquid refrigerant. The provision of a substantially constant, positive pressure of cool gas to the compressor suction of a refrigeration apparatus is still another object of the invention. Other objects and advantages will be apparent to one skilled in this art upon study of this disclosure including the detailed description of the invention including the drawing wherein:

The sole figure is a schematic flow diagram of a refrigeration apparatus having incorporated therein one embodiment of the invention.

In the drawing liquid refrigerant 10' is evaporated in evaporator 11 to refrigerate fluid circulated via conduits 12 and 13 through heat exchanger 14. Refrigerant vapors are Withdrawn from evaporator 11 via conduit 15 and passed to the suction of first stage compressor 16. The first stage compressor discharge is passed via conduit 17 to the suction of second stage compressor 18. The second stage compressor discharge passes via conduit 19 and cooler 21 to accumulator 22. Accumulator 22 discharges via conduit 23 into liquid-gas separator 24 and gas separated from the liquid is passed via conduit 25 to the suction of second stage compressor 18. Expansion valve 20 in conduit 23 is controlled by liquid level controller 30 on separator 24. The pressure in separator 24 is maintained lower than that in accumulator 22 and higher than that in evaporator 11. Liquid in separator 24 is passed via conduit 26 and expansion valve 27 to evaporator 11. Valve 27 is controlled by liquid level controller 28.

A portion of the second stage compressor discharge is utilized as compressor recycle gas and passes via conduit 31, containing valve 32 and aspirator 33, to the gas phase space of evaporator 11. Liquid refrigerant is supplied from evaporator 11 to aspirator 33 via conduit 34.

Suction pressure is maintained constant by press re controller 35 which opens valve 32 as pressure in conduit 15 drops as indicated by pressure tap 36 in conduit 15. When valve 32 is full open and pressure in conduit 15 drops pressure controller 35 opens valve 37 in conduit 38 to bypass a portion of hot gas around aspirator 33 and evaporator 11.

The temperature of the liquid in evaporator 11 is recorded by temperature recorder 39. Liquid can be moved from evaporator 11 via conduit 41 and valve 42. If a mixture is used as refrigerant the ratio of the components in the mixture can change with use and the temperature of the, liquid in evaporator 11 will indicate such change. Commercial propane contains ethane and butane in varying amounts. Ethane will tend to escape from the system more rapidly than the other hydrocarbons so that the ratio of butane to propane will increase and thereby decrease the efficiency of the refrigeration apparatus. An increase in the ratio of butane to propane in the system will be indicated by a rise in the temperature of the liquid in evaporator 11 because the pressure in evaporator 11 will be maintained constant to provide constant suction pressure to compressor 16. When temperature recorder 39 indicates that concentration of heavy constituents in the refrigerant is sufii-cient to impair the efficiency of the system liquid can be withdrawn from evaporator 11 via conduit 41 and fresh refrigerant can be added via that same conduit.

The invention will now be described with reference to a refrigeration system wherein substantially pure propane is the refrigerant in refrigeration apparatus utilized to cool compressed propane vapors taken from an atmospheric pressure propane storage reservoir for return to the reservoir. The refrigerant in evaporator 11 is maintained at about atm-ospheic pressure and about -44 F. so that the suction pressure to the first stage compressor 16 is about atmospheric. The discharge pressure of com- 'essor 16 is about 63 p.s.i.a. and the discharge pressure fcompressor 18 is about 275 p.s.i.a. The pressure on parator 24 is about 63 p.s.i.a.

Pressure controller 35' starts to open valve 32 as the .essure in conduit 15 begins to drop below atmospheric ressure (14.7 -p.s.i.a.) and if the pressure in conduit 15 )ntinues to drop after valve 32 is full open, pressure )ntroller 35 begins to open valve 37 so as to introduce 3t compressed gas via conduit 38 to conduit 15.

The above system has operated successfully in a comiercial installation for the storage of propane at atmosheric pressure.

A similar system has operated successfully utilizing Jmmercial propane containing varying amounts of butane nd ethane as impurities. In this system the evaporator operated at 15 F. and 50 p.s.i.a. The suction pres- 1re of the first stage compressor is 50 p.s.i.a., the suction ressure to the second stage compressor is 120 p.s.i.a. and 1e discharge pressure of the second stage compressor is 75 p.s.i.a. Ethane escapes from the system proporonately more rapidly than do propane and butane and ierefore the ratio of butane to propane in the system :nds to increase. Liquid is pressured from the evapoator periodically and replaced with fresh refrigerant quid in order to maintain the efliciency of the apparatus t a desired level.

That which is claimed is:

1. The method of maintaining a predetermined, subtantially constant pressure on the suction of a compresor in a refrigeration apparatus comprising a compresor, condenser and evaporator which method comprises Iassing a portion of hot compressed gas from the omressor to the suction of the compressor in an amount ufiicient to maintain a predetermined suction pressure in said compressor; and contacting said hot. compressed ;as with a sufiicient amount of liquid withdrawn from.

aid evaporator to cool said gas.

2.. The method of supplying cool recycle gas at a subtantially constant suction pressure to a compressor in t refrigeration apparatus wherein a refrigerant gas is comiressed, condensed and expanded into an evaporator which :omprises withdrawing a portion of hot compressed gas 'rorn the compressor discharge; contacting said hot gas vith a sufficient amount of liquid refrigerant withdrawn rom said evaporator to cool said gas to about the temierature of the liquid refrigerant; passing the cooled gas v0 the evaporator space of the evaporator in an amount :ui'ficient to maintain the gas in the vapor space of the :vaporator at a desired compressor suction pressure; and passing hot, compressed gas directly from the compressor discharge to the compressor suction in an amount sufficient to maintain the desired compressor suction pressure when the pressure of thecooled gas is below the desired suction pressure.

3. Refrigeration apparatus comprising a compressor, a condenser, an evaporator. containing a gas space and a liquid space, first conduit means to pass a first'portion of compressed gas to said condenser, means to pass condense-d gas to said evaporator, second conduit means to pass gas from said evaporator to the suction of said compressor, third conduit means containing a flow controller to pass a second portion of compressed gas to the gas space of said evaporator, liquid-gas contactor means to contact said second portion of compressed gas, prior to its passing to said gas space, with liquid withdrawn from said evaporator, pressure sensing means operatively connected to the suction of said compressor, and pressure control means operatively connected to the pressure means and to the how controller of the third conduit means to pass the second portion of compressed gas so as to control the flow of gas in response to a signal from said pressure sensing means.

4. The apparatus of claim 3 including a fourth conduit means containing a flow controller connecting said first conduit means and said second conduit means; and wherein said pressure control means is also operatively connected to the flow controller in the fourth conduit means so as to pass additional gas to said second conduit means whenthe third conduit means does not supply sufficient gas to maintain the desired compressor suction pressure.

5. The apparatus of claim 3 wherein said means to pass condensed gas to said evaporator contains a liquidgas separator wherein the pressure maintained therein is intermediate that of the compressor suction and that of the compressor discharge.

References Cited by the Examiner UNiTED STATES PATENTS 2,252,200 8/1941 McGrath 62l96 2,551,666 5/1951 Gilmore 62114 X 2,679,730 6/1954 Kobold 62-53 X 3,092,976 6/1963 Tafreshi 62-117 X 3,093,976 6/ 1963 Walcutt 62-l96 3,210,955 10/1965 Anderson et al. 62-117 FOREIGN. PATENTS 577,447 5/ 1933 Germany.

LLOYD L. KING, Primary Examiner. 

1. THE METHOD OF MAINTAINING A PREDETERMINED, SUBSTANTIALLY CONSTANT PRESSURE ON THE SUCTION OF A COMPRESSOR IN A REFRIGERATION APPARATUS COMPRISING A COMPRESSOR, CONDENSER AND EVAPORATOR WHICH METHOD COMPRISES PASSING A PORTION OF HOT COMPRESSED GAS FROM THE COMPRESSOR TO THE SUCTION OF THE COMPRESSOR IN AN AMOUNT SUFFICIENT TO MAINTAIN A PREDETERMINED SUCTION PRESSURE ON SAID COMPRESSOR; AND CONTACTING SAID HOT COMPRESSED GAS WITH A SUFFICIENT AMOUNT OF LIQUID WITHDRAWN FROM SAID EVAPORATOR TO COOL SAID GAS. 